四川理塘萨玛隆洼花岗闪长斑岩地球化学及年代学研究

发布时间：2018-01-26 15:31

  本文关键词： 花岗闪长斑岩 岩石地球化学 锆石U-Pb定年 义敦岛弧 俯冲作用　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：中国三江造山带中段的四川理塘地区,大地构造位置上处于印度板块与欧亚板块结合部位的特提斯构造域东段,属甘孜-理塘弧盆系范畴,横跨甘孜-理塘结合带和义敦-沙鲁里岛弧带两个主要构造单元。义敦-沙鲁里岛弧带是以措交马、冬措等巨型岩基为主体,宏观上呈倒转“S”形的花岗岩带,经历了多期、多阶段复杂的板块构造演化,具有良好的成矿地质环境,形成了十分丰富矿产资源,与花岗岩有关的矿产主要有铅、锌、锡、银、金和稀有元素等。本文以岛弧带上萨玛隆洼岩体为研究对象,通过岩相学、岩石地球化学和年代学等方面的研究,讨论其岩浆起源、形成构造背景及其地质意义。萨玛隆洼岩体岩性为灰白色块状花岗闪长斑岩,侵入于上三叠统图姆沟组砂板岩中。6件样品SiO2含量为61.59%-63.38%,属中酸性岩类,高钾钙碱性—钾玄岩系列。若排除蚀变对分析结果的影响,萨玛隆洼花岗闪长斑岩具有准铝质、高钾、富钠、贫钛的特征。花岗闪长斑岩样品稀土元素含量较高,∑REE=152.61×10-6-167.53×10-6,平均为157.75×10-6;稀土元素配分曲线为轻稀土富集、重稀土亏损的右倾模式;δEu为0.65-0.76,具有弱负Eu异常。在微量元素蛛网图上,花岗闪长斑岩具有类似的曲线特征,均富集Rb、Th、K等大离子亲石元素(LILE),亏损Nb、Ta、Ti、P等高场强元素(HFSE),表明其岩浆起源与板块俯冲作用有关。获得花岗闪长斑岩的锆石U-Pb加权平均年龄为220.1±1.4Ma,为晚三叠世诺利期,代表了其形成年龄。结合前人研究认为,甘孜—理塘洋于早石炭世已经发育洋壳,并于二叠纪-早三叠纪进入洋盆扩张最大阶段,可能于中三叠世洋盆开始萎缩,洋壳由东向西俯冲,引起地幔部分熔融,大量的玄武质岩浆底侵形成玄武质地壳。洋壳俯冲持续至晚三叠世并达到高峰,地幔持续不断的底侵作用使得早期阶段形成的玄武质地壳发生局部熔融,沿着岩浆通道上涌到上地壳的近地表,冷凝结晶形成了萨玛隆洼花岗闪长斑岩体。晚三叠世花岗质岩浆岩的侵入为研究区各元素异常的形成提供了物质来源。研究区内元素异常主要与中酸性岩浆热液活动有关,在中酸性岩体与围岩接触的角岩化带附近是找矿的有利部位。
[Abstract]:The Litang area of Sichuan Province in the middle part of the Sanjiang orogenic belt in China is located in the eastern segment of the Tethys tectonic domain where the Indian plate and the Eurasian plate are combined, belonging to the Ganzi-Litang arc basin system. There are two main tectonic units across the Ganzi-Litang combination zone and the Yiduang-Shaluli island arc belt, which are dominated by giant rock bases such as Cuojiaoma and Dongchao. The inverted "S" -shaped granite belt has undergone multi-stage and multi-stage plate tectonic evolution, has a good metallogenic geological environment, and has formed very rich mineral resources. The main minerals related to granite are lead, zinc, tin, silver, gold and rare elements. The origin, tectonic setting and geological significance of the magma are discussed. The lithology of the Samarong depression is grayish-white granodiorite porphyry. The SiO2 content of the 6 samples intruded into the sand slate of the Upper Triassic Tumigou formation is 61.59 and 63.38, which belongs to the intermediate-acidic rocks. If the influence of alteration on the analysis results is excluded, the Samaronwa granodiorite is of quasi-aluminum, high potassium and rich sodium. The REE content of granodiorite porphyry samples is high, 鈭，

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